#define  _CRT_SECURE_NO_WARNINGS
#include <stdio.h>
int main()
{
	float r1 = 0.0f;
	float r2 = 0.0f;
	float r3 = 0.0f;//标准初始化
	scanf("%f%f", &r1, &r2);
	r3 = (r1 * r2)/(r1+r2);
	/*r3 = 1.0 / ((1.0 / r1) + (1.0 / r2));*/
	printf("ĵֵΪ %.1f\n", r3);
	return 0;
}